Parallel wire strand

ABSTRACT

A parallel wire strand is made, preferably with the casts of the individual wires matched against each other in opposed relationship to form a &#34;balanced&#34; strand, and subsequently reeled upon a reel by rotating or allowing the parallel-wire strand to rotate from side to side about its longitudinal axis as it is reeled to provide a conveniently transportable reel of parallel-wire strand with the strand coiled upon the reel with periodic, alternate clockwise and counterclockwise rotation about the longitudinal axis of the strand.

Sept. 1, 1970 Filed Aug. 25, 1966 J. L. DURKEE ET AL 3,525,579

PARALLEL WIRE STRAND 4 Sheets-Sheet 1 0000/0 f. Dun/0,0

' INVENTORS Q c/ac/fson L. Our/fee flrf/zur E 5e/ '9/;/ey

Sept 1970 J. L. DURKEE ETAL 3,526,57

PARALLEL WIRE STRAND 4 Sheets-Sheet 2 Filed Aug. 25, 1966 INVENTORS Joe/(son L. Dar/fee Sept I, 197% DURKEE ETAL 3,526,57@

PARALLEL WIRE STRAND Filed Aug. 25, 1966 4 Sheets-Sheet 5 J. L. DURKEE ET AL PARALLEL WIRE STRAND 4 Sheets-Sheet 4 Sept. 1, 1970 Filed Aug. 25, 1966 United States Patent C) 3,526,570 PARALLEL WIRE STRAND Jackson L. Durkee, Bethlehem, and Arthur F. Beighley and Donald E. Dunlap, Williamsport, Pa., assignors to Bethlehem Steel Corporation, a corporation of Delaware Filed Aug. 25, 1966, Ser. No. 575,038 Int. Cl. Ellld 21/00 US. Cl. 161-175 Claims ABSTRACT OF THE DISCLOSURE A prefabricated wire strand having a plurality of wires disposed in substantially parallel relation to the axis of the strand, and to each other, the cast of substantially every wire of the strand being counterbalanced by the cast of another wire, and the individual wires being secured against rotational movement at least at two longitudinally separated points.

This invention relates to prefabricated parallel wire strands, and more particularly to prefabricated parallel wire structural strands with superior physical properties.

As used herein, the term structural strand refers to a multi-wire strand used as a substantially fixed permanent structural member. The parallel wire strand of the present; invention has, however, been found particularly useful for building up larger parallel wire structural cables such as are used for the main supporting cables of suspension bridges. This invention will therefore be described with respect to parallel wire strand fabricated for use in the construction of suspension bridge main cables.

Parallel Wire cables are the primary type used for suspension bridges because of their superior strength and axial stiffness over cables made of helical-wire strands, which do not develop the unit ultimate strength or the modulus of elasticity of parallel-laid wires. It has been the practice to construct parallel wire cables in suspension on the bridge by a process known as aerial spinning, that is by hauling individual loops of bridge wire back and forth over the bridge towers and connecting them to the anchorages. A number of such wires are bundled together to form a parallel wire strand. A group of such parallel wire strands are formed consecutively and then compacted together to form the parallel wire suspension cable. Spinning of the parallel wire strands in place on the bridge itself is slow and difficult, and, since it is done under field conditions at a great height, tends also to be dangerous. The length of each individual wire must be carefully adjusted immediately upon erection in order to provide a compact strand with minimum length differentials among the wires as they hang in a catenary across the bridge spans. Attempts have been made to prefabricate the parallel wire strands on the ground at the bridge site, but these efforts have proven unsatisfactory for a variety of reasons. Such strands have often exhibited troublesome tendencies to twist and coil, because of the curvature or cast of the manufactured wire. In addition, it has been thought impossible to reel parallel wire strand so as to make it conveniently transportable, because the maximum-radius strand wires on the reel would presumably be greatly stretched and the minimum-radius wires correspondingly compressed when bent around the drum during reeling.

It is an object of the present invention therefore to paovide a prefabricated parallel wire strand having equallength wires, and method of making the same, such that the strand is stabilized in such manner that it has a minimum tendency to twist and coil.

It is a further object of the present invention to provide a method of continuously reeling parallel-wire strand 'ice as it is fabricated, without harming the individual wires.

We have discovered that the foregoing objects can be attained by forming a hexagonal parallel wire strand in a hexagonal roller die using wires arranged with their casts opposed, pulling the strand through the die by means of a hexagonal clamping device, and securing the strand wires together by resilient binding means; and that such parallel wire strand can be effectively reeled with alternate rotation about the strand axis in opposite directions. We have further discovered that hexagonal parallel wire strand can be continuously made and reeled by the use of a dynamic clamp, i.e. a continuously movable clamp, interposed between the forming dies and the reel.

FIG. 1 shows a plan view of an arrangement according to the present invention for forming parallel wire strand.

FIG. 2 shows a side elevation of the arrangement shown in FIG. 1.

FIG. 3 shows an isometric view of an initial portion of the apparatus.

FIG. 4 shows an elevation of the reeling portion of the apparatus.

FIG. 5 shows a plan view of the portion of the apparatus shown in FIG. 4.

FIG. 6 shows a cross section of one form of the strand of the present invention.

FIG. 7 is a cross-section through the parallel wire strand in FIGS. 3 at 77 showing one roller die.

FIG. 8 is a diagrammatic cross-section through one form of dynamic clamp.

FIG. 9 is a diagrammatic lateral view of the dynamic clamp of FIG. 8 showing supporting structure and one movable element particularly viewed along line 9-9 of FIG. 8.

FIG. 10 is an enlarged diagrammatic cross-sectional view of an alternate dynamic clamp arrangement.

FIG. 11 is a diagrammatic elevation of the alternate dynamic clamp arrangement of FIG. 10.

Referring more particularly to the drawings, a series of turntables 11 and 13 are shown in FIGS. 1, 2 and 3. Each turntable is supported upon a suitable base 15 and is provided with braking means 17 frictionally engaged against drum 18 by any suitable motivating means such as pneumatic cylinder 20 calibrated to place uniform back tension on wire being unwound from the turntable. There may be 91 wires in a typical bridge strand and therefore 91 turntables. For convenience only a few of the tumtables are shown; however, it is to be understood that the remainder would be arranged in the same manner. Turntables 11 have what may be termed left-handed coils of wire mounted thereon and turntables 13 have what may be termed right-handed coils of wire mounted thereon. That is to say, the wire when it is drawn from the top of the turntable will rotate the turntable either clockwise or counterclockwise respectively. The wires pulled off from. turntables 11 are indicated as a group as wires 19, while the wires pulled off from turntables 13 are indicated as a group as wires 21. Wires 19 are pulled throughfairleads 23 and wires 21 are pulled through fairleads 25, except for the wire from the last, or end, turntable in each group, to lay plates 27 and 29, respectively. The wire fromthe last turntable of each group passes directly to the lay plate. As may be seen more clearly from FIG. 3, lay plate 27 has guide holdes in it delineating the left half of a hexagonal pattern and lay plate 29 has guide holes in it delineating the right half of a hexagonal pattern. After passing through the lay plates 27 and 29', the groups of wires 19 and 21 pass through the guide holes in combined lay plate 31 whose guide holes delineate the hexagonal shape of the final strand. There are 91 guide holes in lay plate 31 for a 91-wire strand. It will be noted that all the wires which pass from turntables 11 through lay plate 2.7 pass through the left half of the hexagonal configuration of guide holes in lay plate 31, and that all the wires from turntables 13 which pass through lay plate 29 pass through the right half of the hexagonal configuration of guide holes in lay plate 31.

From lay plate 31 the wires are conducted to a small hexagonal lay plate 32 which directs them into a first roller die 33. As shown in FIG. 7, roller die 33 comprises a base 34, and a support ring 35 in which are resiliently mounted six freely-rotatable rollers 37 alternately displaced into two radial rings each comprised of three rollers 37 so that the roller journals 39 do not interfere with each other, and arranged to delineate a hexagonal die opening. In FIG. 7 one radial ring of rollers 37 is shown in dotted outline where it is partially obscured by the second radial ring of rollers. Rollers 37 are resiliently urged by means of springs 43 attached to each roller mounting 45 against the wires passing therethrough to form a hexagonal strand 41.

From roller die 33 the hexagonal strand 41 passes through further hexagonal roller dies 47, 49, 50, and 51 which may be substantially identical in construction with roller die 33.

From roller die 51 the hexagonal strand passes to a hexagonal dynamic clamp 53, diagrammatically shown in cross section in FIG. 8, and having extended articulated clamping means 55, 87, and 89 designed to cooperate as shown in FIG. 8 so as to place an equal clamping pressure on all sides of the strand. Dynamic clamp 53 may conveniently take the form of a so-called caterpillar-type capstan, or dynamic pulling clamp, having three meshing caterpillar-type tracks each clamping the two of the six flat surfaces of the hexagonal strand. Alternately if desired two dynamic clamps 135 and 137 can be used in tandem as shown diagrammatically in FIGS. 10 and 11. In the event two dynamic clamps 135 and 137 are used as shown in FIGS. 10 and 11, each need only have two articulated clamping surfaces 139 and 141, and 143 and 145 as shown in FIG. 10, which illustrates how the clamping surfaces of dynamic clamp 137 are turned at a 60-degree angle from those of dynamic clamp 135 in order to obtain full strand clamping action.

Dynamic clamp 53 serves to pull the wires from the turntables 11 and 13 through roller dies 33, 47, 49, and 51. In order to pull the wires through the apparatus absolutely evenly it is important that a uniform grip be obtained on each wire of the strand. If one wire is not gripped as tightly as the others this wire may lag behind and the resulting strand will not be composed of wires of equal length. It has been found necessary to use a hexagonal strand shape and pattern of wires such that the wires are in the minimum-void position within the strand. With this configuration, each wire has three lines of contact and clamping as illustrated in FIG. 6. This arrangement provides even clamping and effectively prevents any internal wires of the strand from lagging behind. At the same time roller dies 33, 47, 49, 50* and 51 prevent any external wires of the strand from lagging behind, such as might occur around the inner perimeter of a solid die as a result of friction of the wires against such die. It will thus be seen that the combined use of a hexagonal strand clamping means and a hexagonal roller die with a hexagonal strand, enables the fabrication of parallel wire strands wherein the wires are equally stressed during manufacture of the strand and therefore precisely equal in length. It is not essential that the hexagonal strand be equilateral as an extral layer of wires may be added to any fiat of the hexagon in order to make up a strand of varying numbers of wires. It is necessary, however, that the closely-packed hexagonal structure be maintained as has been explained heretofore.

Dynamic clamp 53, which as illustrated in FIGS. 8 and 9 comprises one suitable form of clamping structure, is comprised of endless articulated clamping surfaces 55, 87 and 89, rotatable upon sprocket wheels 57 and 59, and driven by means of drive shaft 61, and, in the I case of articulated clamping surface 55, meshing bevel gears 63 and 65 which rotate shaft 67 upon which is mounted sprocket wheel 57. Drive shaft 61 is driven through chain 69 by combined motor and gear reducer 71. Gears 73, and 77 serve to rotate shafts 79 and 81 which in turn rotate shafts 83 and 85 upon which are mounted supporting sprocket wheels similar to sprocket wheel 57, and upon which the other two opposing articulated clamping surfaces 87 and 89, shown in partial section in FIG. 8, are rotated. Rollers 91 are journaled on link connecting pins 93 between track links 95 and 97. It will be noted in FIG. 9 that extensions 99 on each alternate link 97 overlap similar extensions 101, shown in dotted outline, on each adjacent link 95 to enable pins 93 to connect and articulate the links. Sprocket wheels 57 and 59 with their shafts are journaled in supporting plates 103 and 105 secured to end plates 107 and 109 by brackets 104. Also mounted between supporting plates 103 and 105 is an outer track element 111 upon which rollers 91 travel. Brackets 1 13 and 115 are mounted on the outside of supporting plates 103 and 105. Shafts 117 pass through brackets 113 and 115 in sliding relationship therewith to support two movable inner track elements 119 and 121 which are urged inwardly by springs 123 against links 95 and 97 as they pass along the parallel-wire strand 41 to urge the clamping faces of the links 95 and 97 against the parallel wire strand as shown in FIG. 8. Nuts 125 on shafts 117 prevent tracks 119 and 121 from being forced inwardly too far. An upper section 127 of end plates 107 and 109 may be arranged to separate along line 129 so that one whole track assembly may be thrown back to facilitate threading of the parallel wire strand through the clamp. If desired, hydraulic means may be used in place of, or in addition to, springs 123 to urge the tracks and clamping links 95 and 97 against the strand 41, and, in this case, the strand may be threaded by opening the tracks by the operation of the hydraulic means sufiiciently to allow threading to take place. If a mechanical sleeve splice on a wire passes through the dynamic clamp, first track element 119, and then track element 121 will lift to allow the splice to pass through. It will be seen that while one track is lifted the other will provide efficient clamping action so that the internal wires in the strand will not slip with respect to each other.

In the event two dynamic clamps are used as shown in FIGS. 10 and 11, each clamp may have only one pair of articulated clamping surfaces. The articulated clamping surfaces 143 and 145 of dynamic clamp 137 are turned at a 60-degree angle with respect to articulated clamping surfaces 139 and 141 of dynamic clamp as illustrated in FIG. 10. Articulated clamping surfaces 139, 141, 143 and 145 are composed of connected track links 147 and 149 comparable to track links 95 and 97 of dynamic clamp 53 except that each track link carries three clamping faces engaging three sides of the hexagonal strand rather than two clamping faces as in the construction of dynamic clamp 53. Other than this, the construction of the two articulated clamping surfaces of dynamic clamps 135 and 137 are substantially the same as that of three-track dynamic clamp 53 and the same part numbers have been used where applicable in the figures.

As the parallel wire strand is drawn through the roller dies it is bound at intervals with a securing material 128 at binding stations located between the roller dies. This may be done by stopping the strand every few feet and applying suitable tape manually at points between adjacent roller dies, or alternatively a suitable mechanical traveling taping device may be used to tape the strand while the strand is moving. When a mechanical taping device is used it will be possible to use fewer roller dies. If manual taping is done it may be desired to increase the number of roller dies in order to increase the number of taping stations. Suitable variations will occur to those skilled in the art. Normally taping the strand at threefoot intervals will be found effective in maintaining the strand wires in a compact cross-sectional shape during subsequent strand evolutions such as reeling and erection.

allowing the wires of the strand to become unduly disarranged. It is highly desirable for the tape to be resilient enough to return at least partially to its former length when tension is reduced. A tape which has been found very suitable is a rayon-reinforced plastic tape After the strand is drawn through dynamic clamp 53, 5 wherein a rayon yarn or filament reinforcing is mounted firmly secured between the extended clamping surfaces in an acetate or polyester film matrix, and a rubber 55, 87 and 89 it is passed to take-up 157 where it is resin backing provides adhesion. Tape of such description reeled onto a large-diameter reel 159. As the strand passes two or three inches wide and .010 inch thick may be to reel 159 it is supported beyond dynamic clamp 53 1O wrapped three times around the strand to comprise each by roller table 163 and then passes across traverse mechabinding 128. Different widths or numbers of wraps may nism 16 1 which directs the strand onto reel i159 mounted be used to provide whatever strength is required for on shaft 160 which is journaled in bearings 162 in mountthe particular strand being fabricated depending upon ing 164, and prevented from rotating independently of the number of the wires comprising the strand. The tape shaft 160 by keepers 158. A motor 165 operates traverse 5 should also provide good abrasion resistance. The follow- 161 through suitable drive means, gear reducer 166, and ing tables give examples of the important properties of chain 167 which moves traverse carriage 168 on which the most suitable, and two unsuitable tapes for comare mounted horizontal and vertical roller guides 170 parison.

Length at Percent Length at return to Perm. Percent Load at stretch Test Sample No. Load lb. load, in. no load, in. set, in. return break, lb. at break Suitable rayon-reinforced acetate tape 25 10% 10 100 160 50 105 10 0 100 165 6. 10% 10 52 $52 170 5. 66 1055 10%-z 552 58.2 17755 7.18 10 16 10% 55 45. 4 180 5. 88 1028 105 /52 "/52 39. a 180 s. 25 175 11%, 10 m ,45 29. 4 179 a. 25

Unsuitable glass-filament reinforced acetate tape 50 10W 10 0 100 395 5. 53 100 10 ,5 10 /52 ,52 75 394 4. 38 150 10% 10552 L52 75 390 4. as 200 10% 10 0 100 ass 250 10552 10 0 100 391 3. 75 300 10515 10 0 100 397 a. 75 350 10 52 10 0 100 39s a. 75 400 385 a. 75

Unsuitable vinyl plastic tape 5 11 10%;; /52 90. 5 23 135. 25 10 1275 10% at 87. 0 22% 137. 15 15 ,5 10% 4 s5. 7 2255 135. 25 20 19MB 11 ,5 87.6 2352 25 23 123.75

and 172. A motor 169 operates reel 159 through appropriate gearing in gear reducer 17 1, chain 173, clutch and brake disk 177.

It has always been considered impractical to reel parallel wire strand because the wires on the shorter inner circumference presumably could not be adjusted to the Wires on the longer outer circumference of a reeled parallel wire strand without inducing excessive stress in the individual wires. This is a particular disadvantage in a strand to be used in a bridge cable since the strand wires must be maintained precisely equal in length, and overstressing and kinking of wires would be intolerable. It has been discovered, however, that a parallel wire strand may be reeled effectively if the strand is bound at intervals as described above with a resilient securing means which will stretch sufiiciently to allow the strand to open up slightly as it is reeled, but insufficiently to allow the wires in the strand to become a loose bundle of wires, and, in addition, if the strand is rotated or allowed to rotate in alternate directions about its own axis through a range of approximately 270 degrees as it is reeled. It is not necessary to actively rotate the strand, since effective, though somewhat uneven, rotation will be obtained by merely allowing the strand free rein to rotate of its own accord.

The binding tape must have sufiicient strength so that it will not break as it confines the wires of the strand during reeling, and it must have a maximum stretch of not over about 10% in order that it can permit the wires to open or spread sufficiently to adjust the stresses in the strand during reeling, without at the same time A satisfactory parallel wire strand can be fabricated according to the present invention by first clamping the leading ends of the wires into a hexagonal strand shape by means of a suitable hexagonal clamp and then drawing the strand through the roller die 33 and the succeeding roller dies by means of a towing line attached to the clamp. Alternatively, a socket may be attached to the end of the strand and the towing line attached thereto for drawing the strand forward.

Because of the longitudinal stresses occasioned in th individual wires of the strand by reeling, however, it is necessary that any reeling operation be isolated in some manner from the forming operation so that the strand distortions and stresses incident to bending of the strand during reeling will have no disturbing effect on the wires at the forming die. Such isolation may be attained if the reeling operation is separated from the die by an appropriate distance sufficient to effectively separate the two operations. Alternatively, die forming and reeling can be done in separate operations. It will readily be understood that this is inconvenient, particularly if the two separate operations are resorted to and the strands are very long.

Fabrication and reeling of the strand, however, may be done as a continuous unitary operation if a hexagonal parallel wire strand is formed in a hexagonal die, and then passed through a hexagonal dynamic clamp, as illustrated, to the reel. The dynamic clamp effectively isolates the fabrication operation from the reeling operation so that the reeling of the strand does not adversely afiFect the fabrication. It is most satisfactory if this is done by means of a hexagonal dynamic clamp which is also a capstan such as a caterpillar-type capstan as illustrated in FIGS. 8 and 9, or 10 and 11. The effective isolation of the two operations is provided by the combined use of a hexagonal dynamic clamp with a hexagonal strand so that the wires of the strand are securely gripped and prevented from moving longitudinally relative to each other in the forming section of the apparatus due to the stresses incident to bending the strand on the reel.

As the parallel wire strand leaves the clamping surfaces of dynamic clamp 53 or dynamic clamps 135 and 137, the strand is allowed, or encouraged, to rotate about its own axis in alternating directions as may be seen in FIGS. 4 and 5, as it passes onto reel 159, Where, as may be seen in FIG. 5, it is spooled alternately from side to side on the reel in as many layers as may be required. The alternating strand rotation, and the resilience of the tape securing the strand, relieve the distortions and stresses incident to reeling the strand and allow the strand to be reeled without damage. The strand must not be hampered in commencing to rotate as it approaches the reel.

It will be seen in FIGS. 1, 2 and 3 that Wires 19 derived from turntables 11 upon which left-hand wound coils are mounted will tend to have a cast or natural curvature opening toward the left-hand side of the apparatus, as viewed in FIG. 3, while wires 21 derived from turntables 13 will have a cast or natural curvature opening towards the right-hand side of the apparatus as viewed in FIG. 3. In the present invention these curvatures are maintained in the same directions as the strand is fabricated, and the finished strand, therefore, has all the Wires arranged in the strand with their natural casts or curvatures in the same direction with respect to each other as they are when on the turntables. As a result, the cast of the wires is eifectively balanced in the strand, so that the strand itself has no tendency to twist or coil.

When beginning the formation of the strand the leading ends of the individual wires are first clamped together with their natural casts or curvatures arranged in the same directions as the Wires are coiled on the turntables. This may be conveniently done by placing a right-angle bend in the end of each wire and securing it on a board or other flat surface by stapling, or otherwise, in the radial position which it is to maintain in the strand with respect to the other wires in order to maintain the natural curvatures of the wires in the desired opposing directions, and then attaching a portable clamp, or the dynamic clamp, around the strand a short distance away from the board. The board and the attached bent wire ends may then be severed from the end of the strand.

Full-strength-type socketing may be done by bending the end of the strand upwards, inserting the end in a molten-metal-type socket, spreading the individual wires, and pouring in the appropriate molten metal. It will be realized that the Wires must be securely clamped together behind the clamp before this can be done, in order that wires will not slip relative to one another during socketing. The socket may then be fastened to the reel in order to begin reeling. The wires of the fabricated strand will then still be arranged with their natural casts evenly opposed or balanced, with the result that the strand will be found to be free from all tendency to twist and coil. In order to unreel the wire efiiciently it is desirable that the wire coils on the turntables 11 and 13 be respectively left-handed and right-handed coils so that the leading end of the Wires leaves the coil from the top. When the length of strand which it is desired to make has been completed the strand must also be securely clamped or socketed at the terminal end so that in the completed strand the wires are securely held at both ends and the balance of wire cast is not lost.

The cast of the wires need not all be arranged in one of two directions as illustrated, nor need each wire be grouped together with all the other wires having a cast maintained in the same direction, so long as each wire having a cast maintained in one direction is substantially balanced by another strand wire having its cast maintained in the opposite direction. For instance, the wires may be mixed together with casts opposing in two, three, or four or more directions. The strand and method of formation as illustrated and described has been found very desirable and practical, however.

If the precise, even lengths of the individual wires in the strand are not so critical for a particular application as they are for the usual structural strand such as bridge suspension strand, and/or the strand does not need to be reeled, it is not necessary that a hexagonal strand be formed or that roller dies and a hexagonal clamp be used in order to form a stabilized parallelwire strand according to the present invention, as the pairing of the natural curvatures of the individual wires in the strand may also effectively be made in a round or other configuration of strand where such strand may be desirable for a particular purpose.

Prefabricated parallel wire strands made in accordance with the present invention are extremely stable with negligible tendency to twist or curl, and when used for the construction of parallel-wire suspension bridge cables exhibit greater uniformity of individual wire lengths when suspended between the bridge towers than is normally attainable in strands spun-in-place on the bridge.

We claim:

1. A parallel wire strand comprising:

(a) a plurality of wires disposed in substantial parallel relation to the axis of the strand and to each other, at least some of said wires having a longitudinal residual bending moment, or cast, derived from a previous longitudinal bending operation,

(b) the individual wires being secured against rotational movement at least at two longitudinally separated points,

(0) the longitudinal residual bending moment in any direction of substantially every wire of the strand being counterbalanced by another wire the longitudinal residual bending moment of which is disposed in substantially an opposite direction to provide a stabilized strand.

2. A wire strand according to claim 1 wherein the strand has a substantially hexagonal cross-section.

3. A wire strand according to claim 1 in which all wires having a longitudinal residual bending moment disposed in one direction are grouped together in one portion of the strand cross-section and are opposed to a substantially equal number of wires having their longitu dinal residual bending moments disposed in the opposite direction grouped together in another portion of the strand cross-section.

4. A wire strand according to claim 2 in which substantially one-half the wires in the strand have a lon gitudinal residual bending moment disposed in one direc tion and are grouped in one portion of the strand crosssection and the remainder of the wires have a longitudinal residual bending moment disposed in the opposite direction and are grouped in the remainder of the strand cross-section.

5. A wire strand according to claim 4 secured at intervals with a resilient binding means having an extensibility of 5 to 10 percent and at least a 20% return to original length following stressing to of its breaking strength and a 50% return to original length following stressing to 5 0% of its breaking strength.

References Cited UNITED STATES PATENTS 334,709 1/1886 Kruesi et al. 57-7 1,157,500 10/1915 Brackevbohm 57l0 (Other references on following page) 9 UNITED STATES PATENTS Howe 14-22 X Robinson 14-22 Thomas 57-138 Seeley 22 6-172 Howe et a1. 57-160 Gilmore 174-130 Bowers 57-145 10 FOREIGN PATENTS 528,466 4/1939 Great Britain.

ROBERT F. BURNETT, Primary Examiner 5 R. L. MAY, Assistant Examiner US. Cl. X.R. 

